Anti-HIV-1 positive antisera were tested for their ability to lyse HIV-1 infected cells in the presence of complement. We will test a panel of anti- HIV-2 positive human sera for their ability to activate human complement by the classical pathway using HIV-2 infected cells. Activation will be assessed by the flow cytometric detection of cell surface C3 deposition using C3-IgG conjugated to FITC. Analysis of complement-mediated cytolysis of infected cells using defined antisera against recombinant HIV-1 env or core antigens suggested that the env gp160/120 and p24 (gag) act as target antigens for antibody and complement mediated cytolysis. Cooperative effects of specific antibodies and complement inhibited HIV infection. We will compare the relative efficiencies of human positive sera and monospecific rabbit sera for their roles in complement mediated lysis of HIV-2 infected cells.